1. Field of the Invention
The present invention relates to an antenna device, more particularly to an antenna device having a dual-band antenna.
2. Description of the Related Art
In recent years, popularity of the Internet accelerated development of Wireless Wide Area Networks (WWAN) for city-to-city or even country-to-country mobile access. WWAN use several frequency bands, two of which have frequencies ranging from 824 MHz to 960 MHz and from 1710 MHz to 2170 MHz, respectively. Accordingly, most modern portable computers, such as laptop computers, notebook computers, and netbook computers are equipped with an antenna device for access to WWAN.
It is known that size, weight, and thickness of portable computers have to be carefully designed so as to avoid compromising mobility. Hence, conventional monopole antennas, spiral antennas, and loop antennas are becoming less suitable for use in modern portable computers due to their dimensions. Referring to FIG. 1, a planar inverted-F antenna 9 for portable computers has been proposed to overcome this issue. Nevertheless, the planar inverted-F antenna 9 is known to have narrow bandwidth, low efficiency, and directional antenna radiation pattern.